A model test apparatus and method for analyzing the influence of seepage force on sediment initiation under wave-current action.

Abstract

This invention discloses a model test apparatus and method for analyzing the influence of seepage force on sediment initiation under wave-current action. The apparatus includes a horizontal water tank made of plexiglass, a wave-current generator, a seepage force generator, and a data acquisition module. The combined reciprocating motion of a first and second piston installed at the end of the horizontal water tank creates a reciprocating flow to simulate wave motion. A circulating water system is added to simulate the combined effect of wave and current. A first water reservoir simulates different water depths through air pressure regulation. The seepage force generator is used to place sediment samples and generate seepage force with a specified distribution. The data acquisition module is used to collect the data required for the experiment. The sediment initiation process is observed using a high-definition digital imaging device combined with image processing technology. This invention has the advantages of small footprint, convenient operation, and precise control.

Description

Technical Field

[0001] This invention relates to a marine geotechnical engineering model test apparatus, and more particularly to a model test apparatus and method for analyzing the influence of seepage force on sediment initiation under wave and current action. Background Technology

[0002] The foundation structure of offshore structures is subject to scouring due to the combined action of waves and currents, resulting in shallower foundation depths and potential engineering safety hazards. Sediment initiation represents the initial critical state of scouring, and its study is crucial for understanding the evolution of scouring depth and for prevention. Under wave-current action, the seabed experiences periodic oscillating currents. Different depths of seabed soil, due to varying cumulative pore water pressure amplitudes, create pressure gradients, inducing seepage from within the seabed towards the surface. The sediment initiation pattern at this point differs significantly from that of steady-state flow. Currently, most experiments utilize large wave-current flumes, but these experimental setups are large, typically around 50 meters in length, and lack flexibility. Fluid surface fluctuations during wave generation also significantly impact high-speed photography and subsequent image processing. Furthermore, wave-current flumes are difficult to analyze independently of the upward seepage force, which significantly influences sediment initiation. Therefore, designing a model experimental device to analyze the influence of seepage force on sediment initiation under wave-current action is both necessary and urgent.

[0003] The challenge of the experiment lies in how to separate the upward seepage force generated by the waves and actively and precisely control it, while achieving functionality within a relatively small size. This is the problem that this application focuses on solving. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a model test device and method for analyzing the influence of seepage force on sediment initiation under wave action, which has a small footprint, is easy to operate and has precise control.

[0005] To address the above technical problems, this invention provides a model test device for analyzing the influence of seepage force on sediment initiation under wave-current action, comprising: a horizontal water tank device, a wave-current generating device, a seepage force generating device, and a data acquisition module.

[0006] The horizontal water tank device is the main part of the experimental apparatus, and its material is transparent plexiglass. The horizontal water tank device includes a first connecting part, a first rectifying part, an experimental observation part, a second rectifying part, and a second connecting part. The first and second connecting parts include the corner sections of the water tank and are connected to the wave-generating unit and the circulating water pipeline; the first and second rectifying parts are equipped with honeycomb rectifiers; the bottom of the experimental observation part is detachable, which facilitates the installation of a seepage force generating device.

[0007] The wave-current generating device includes a wave-generating unit and a steady-flow circulation unit. The wave-generating unit is used to generate an oscillating water flow that simulates wave action, and the steady-flow circulation unit is used to simulate a steady water flow that simulates ocean current action.

[0008] The wave-generating unit controls the formation of the oscillating flow through the combined reciprocating motion of the first piston and the second piston. The oscillating flow is controlled by the combined reciprocating motion of the first piston and the second piston. The first piston is connected to the first connecting part, and the second piston is connected to the second connecting part. The two pistons are linked by a piston connecting rod. The amplitude and speed of the piston movement are controlled and adjusted by the electro-hydraulic servo control system. The hydraulic power mechanism of the electro-hydraulic servo control system drives the piston connecting rod so that the two pistons reciprocate according to the input amplitude and period.

[0009] The stable water flow is maintained by a stable flow circulation unit, which includes a first sealed water tank, a first air compressor, a circulating water pump, a flow meter, a one-way valve, and circulating water pipelines. The first air compressor is connected to the top of the first sealed water tank via an air pipeline, and the water pressure is controlled by changing the air pressure to simulate the wave effect at different depths.

[0010] The seepage force generating device is used to place sediment samples and generate seepage forces with a specified regular distribution. This device can isolate the upward seepage force generated by waves, accurately apply periodically varying upward seepage forces, and analyze their impact on sediment initiation independently. The seepage force generating device includes a sediment tank, permeable stones, a second sealed water reservoir, a second ball valve, a second pressure gauge, and a second air compressor. A sediment cushion layer is laid at the bottom of the sediment tank, and permeable stones are placed on top of the sediment cushion layer. Sediment samples used to observe sediment initiation are laid on the permeable stones. A second ball valve is located at the bottom of the sediment tank and connected to the second sealed water reservoir. The second sealed water reservoir is connected to the second air compressor. The second ball valve controls the switch, adjusting the air pressure to change the water pressure and control the magnitude of the seepage force. The air pressure changes are recorded by the second pressure gauge.

[0011] The data acquisition module includes a first pore water pressure gauge, a second pore water pressure gauge, and a Doppler ultrasonic velocimeter. The first pore water pressure gauge is placed on top of the sediment sample to measure the pore water pressure at the sediment bed surface; the second pore water pressure gauge is placed 5 cm below the sediment bed surface to measure the pore water pressure at that location. The probe of the Doppler ultrasonic velocimeter is fixed at the center of the side wall of the experimental observation section to measure the flow velocity. The data acquisition system also includes a support, LED lighting, and a high-definition digital imaging device. The support is fixed to the upper side of the experimental observation section of the horizontal water tank device, and the LED lighting and high-definition digital imaging device are mounted on the support for photographing the experimental process.

[0012] Simulation experiments were conducted using the above-mentioned apparatus. First, the valve at the bottom of the sediment tank was closed to prevent seepage force. Under the designed water depth and wave flow conditions, the sediment initiation was captured using a high-definition digital imaging device. The flow velocity distribution and pore pressure changes at the positions of the first and second pore pressure gauges were collected. The pressure gradient was obtained by subtracting the data collected from the two pore pressure gauges, and thus the seepage force change curve was plotted. Subsequently, the experiment was repeated, maintaining a stable flow while stopping the piston reciprocating motion to obtain the sediment initiation under stable flow conditions. Then, the valve at the bottom of the sediment tank was opened, and the air pressure change was controlled to generate calculated seepage force. The sediment initiation distribution under the action of stable flow plus seepage force was obtained and compared with the sediment initiation under stable flow and wave flow conditions.

[0013] The superior effects of this invention are as follows:

[0014] 1) The reciprocating motion of the first and second pistons at the end of the horizontal water tank device forms a reciprocating flow to simulate wave motion, and the combined effect of wave and flow is simulated by the circulation water system.

[0015] 2) The first sealed water tank simulates the wave and current effects at different depths by controlling the water pressure conditions through changes in air pressure;

[0016] 3) The completely sealed test device avoids the influence of liquid surface fluctuations on high-speed photography;

[0017] 4) The overall structure of the device of the present invention is compact and simple, occupies a small area, is about 3m in length, and is easy to operate and control precisely. Attached Figure Description

[0018] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0019] Figure 1 This is a front view of an embodiment of the present invention;

[0020] Figure 2 This is a top view of an embodiment of the present invention;

[0021] Figure 3 This is a schematic diagram showing the ratio of upward seepage force to upward lifting force within one cycle in an embodiment of the present invention;

[0022] Explanation of the labels in the diagram:

[0023] 1 – First connecting part; 2 – First rectifier part;

[0024] 3 – Cellular rectifier; 4 – Test and observation unit;

[0025] 5 – Second rectifier section; 6 – Second connecting section;

[0026] 7 – Camera system bracket; 8 – High-speed camera;

[0027] 9 – LED lighting system; 10 – First piston;

[0028] 11 – Second piston; 12 – Piston connecting rod;

[0029] 13 – Electro-hydraulic servo control system; 14 – First air compressor;

[0030] 15 – Second air compressor; 16 – First sealed water reservoir;

[0031] 17 – Second sealed water storage tank; 18 – First ball valve;

[0032] 19 – Second ball valve; 20 – Circulating water pump;

[0033] 21 – Silt trough; 22 – Permeable stone;

[0034] 23 – First pressure gauge; 24 – Second pressure gauge;

[0035] 25 – Doppler ultrasonic velocimeter; 26 – First pore water pressure gauge;

[0036] 27 – Second pore water pressure gauge; 28 – Flow meter;

[0037] 29 – Circulating water pipeline; 30 – One-way valve. Detailed Implementation

[0038] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0039] Figure 1 A front view of an embodiment of the present invention is shown. Figure 2 A top view of an embodiment of the present invention is shown. Figure 3 This diagram illustrates the ratio of upward seepage force to upward lifting force over one cycle in an embodiment of the present invention. Figure 1 and Figure 2 As shown, the present invention provides a model test device for analyzing the influence of seepage force on sediment initiation under wave-current action, including a horizontal water tank device, a wave-current generating device, a seepage force generating device, and a data acquisition module.

[0040] The horizontal water tank device includes a first connecting part 1, a first rectifying part 2, a test observation part 4, a second rectifying part 5, and a second connecting part 6. The horizontal water tank device is made of transparent plexiglass for easy acquisition of high-definition images. The test observation part 4 is detachable at both ends and at the bottom. The two ends of the test observation part 4 are connected to the first rectifying part 2 and the second rectifying part 5 respectively via bolts and sealing rings. The bottom of the test observation part 4 is connected to the sediment tank 21 via bolts and sealing rings. Each of the first rectifying part 2 and the second rectifying part 5 is equipped with a honeycomb rectifier 3 to reduce disordered fluctuations in the incoming flow and thus obtain a uniform water flow. One end of the first connecting part 1 is connected to the first rectifying part 2, and the other end is connected to the first piston 10; one end of the second connecting part 6 is connected to the second rectifying part 5, and the other end is connected to the second piston 11. The first connecting part 1, the second connecting part 6, the first piston 10, the second piston 11, and the circulating water pipe 29 are connected, and each connection is sealed with an O-ring.

[0041] The wave generation device includes a wave-generating unit and a stable flow circulation unit. The wave-generating unit includes an electro-hydraulic servo control system 13 and a piston rod 12. The designed motion amplitude and period are input through the electro-hydraulic servo control system 13, such as amplitude A = 15cm and period T = 2s. The output of the electro-hydraulic servo control system 13 is sent to the piston rod 12, with a first piston 10 and a second piston 11 at each end. The first piston 10 and the second piston 11 reciprocate together, driving the water flow in the tank to simulate the oscillation of water flow near the bed surface under wave action. The stable flow circulation unit controls the stable flow velocity to the designed level, such as v = 15cm / s, through a circulating water pump 20 and a flow meter 28. Water flows into and out of the horizontal tank device through a circulating water pipe 29. The connection is sealed with waterproof adhesive and O-rings. A one-way valve 30 is located on the inlet pipe of the circulating water pipe 29 to ensure unidirectional flow of the circulating water. The water flow is collected in the first sealed water storage tank 16, which is connected to the first air compressor 14. The air pressure is adjusted to 25 kPa, 50 kPa, and 75 kPa to simulate water depths of 2.5 m, 5 m, and 7.5 m by the control switch of the first ball valve 18. The air pressure changes are recorded by the first pressure gauge 23.

[0042] The seepage force generating device includes a second air compressor 15, a second sealed water reservoir 17, a second ball valve 19, a second pressure gauge 24, a sediment trough 21, and permeable stones 22. A bedding layer is first laid in the sediment trough 21, and permeable stones 22 are placed on the bedding layer to transmit water pressure. The test sediment sample is then placed on the permeable stones 22. The upward seepage force is controlled by the pore pressure in the sediment sample. The bottom of the sediment trough 21 is connected to the second sealed water reservoir 17 via a pipeline. The second air compressor 15 is connected to the top of the second sealed water reservoir 17, and the second ball valve 19 controls the switch to adjust the air pressure, simulating the magnitude of the seepage force in the sediment sample. The air pressure changes are recorded by the second pressure gauge 24.

[0043] The data acquisition module includes a Doppler ultrasonic velocimeter 25, a first pore water pressure gauge 26, and a second pore water pressure gauge 27. The first pore water pressure gauge 26 is placed on top of the sediment to measure the pore water pressure at the sediment bed surface; the second pore water pressure gauge 27 is placed 5 cm below the sediment bed surface to measure the pore water pressure at that location. The pressure gradient is obtained by subtracting the data collected by the two gauges, thereby plotting the permeability change curve. The probe of the Doppler ultrasonic velocimeter 25 is fixed at the center of the side wall of the experimental observation section 4 to measure the flow velocity. The data acquisition system also includes a camera system bracket 7, a high-speed camera 8, and an LED lighting system 9. The bracket 7 is fixed to the upper part of the experimental observation section 4, and the LED lighting system 9 and the high-speed camera 8 are mounted on the bracket 7 to record the sediment initiation on the top surface of the sediment tank 21.

[0044] The above-mentioned apparatus was used to conduct a simulation experiment to observe the effect of upward seepage force on sediment initiation under wave current. The specific steps are as follows:

[0045] S1. First, clean the horizontal water tank device to achieve good visibility of the acrylic glass. Complete the calibration of the first pore water pressure gauge 26 and the second pore water pressure gauge 27, and install and fix the Doppler ultrasonic velocimeter 25. Fill the sediment tank with non-erodible solid material, and fill the second sealed water reservoir 17 with sufficient water. Connect the sediment tank 21 to the second sealed water reservoir 17, and connect the second sealed water reservoir 17 to the second air compressor 15. Install the stable flow circulation unit, ensuring the entire water tank is full of water, all components are properly connected, and there are no leaks of water or air at any interface.

[0046] S2. Close the valve at the bottom of the sediment tank 21 to keep the seepage force generating device in the closed state. Control the water pressure inside the equipment to the design requirements using the first air compressor 14. Using the data from the circulating water pump 20, flow meter 28, and Doppler ultrasonic velocimeter 25, ensure that the average flow velocity of the stable flow reaches the test control conditions. Then, turn off the circulating water pump 20 and turn on the electro-hydraulic servo control system 13 to drive the first piston 10 and the second piston 11 to reciprocate. Combine the data from the Doppler ultrasonic velocimeter 25 to determine the test control conditions for simulating the wave state.

[0047] S3. Remove the silt trough 21, fill the bottom of the silt trough 21 with a silt and gravel cushion layer of a certain thickness, then place permeable stones 22 on top, and then lay a silt sample of a certain thickness. Place the first pore water pressure gauge 26 and the second pore water pressure gauge 27 on the top surface of the silt sample and 5 cm below the top surface. Finally, install the silt trough 21 onto the test observation unit 4. Ensure the entire trough is filled with water, the pressure provided by the first air compressor 14 is maintained at the level of step S2, all components are properly connected, and there are no leaks of water or air at any of the interfaces.

[0048] S4. Begin the sediment initiation simulation test under wave flow conditions. Keep the bottom valve of the sediment tank 21 closed. Adjust the circulating water pump 20 and the electro-hydraulic servo control system 13 to the stable flow velocity determined in step S2, and adjust the piston movement amplitude and period to meet the test design requirements. Record the sediment initiation situation for a period of time using a high-speed camera 8. Collect data using a Doppler ultrasonic velocimeter 25. Calculate the seepage pressure gradient by subtracting the data from the first pore water pressure gauge 26 and the second pore water pressure gauge 27. The seepage pressure gradient is the same as the seepage force value, thus obtaining the change of the upward seepage force within one cycle.

[0049] S5. Conduct a simulation test on the influence of upward seepage force under wave-flow conditions on sediment initiation. Close the bottom valve of sediment tank 21 and the electro-hydraulic servo control system 13. Keep the circulating water pump 20 unchanged. Under stable flow conditions, record the sediment initiation situation for a period of time using a high-speed camera 8. Then open the bottom valve of sediment tank 21 and adjust the pressure provided by the second air compressor 15. Combine the data collected by the first pore water pressure gauge 26 and the second pore water pressure gauge 27 to adjust the seepage force to be consistent with the periodically changing upward seepage force obtained in step S4. Then calculate the ratio of seepage force to upward lifting force based on the flow velocity collected by the Doppler ultrasonic velocimeter 25 (e.g., ...). Figure 3As shown in the figure, the upward force is the lift force of the water flow on the particles, calculated according to the classical formula of sediment motion mechanics. The sediment initiation situation is recorded by high-speed camera 8 over a period of time. The sediment initiation probability at this time is calculated based on the proportion of sediment washed away from a certain area of ​​the bed surface. This probability is compared with the sediment initiation probability of stable flow without the application of seepage force and the sediment initiation probability obtained in step S4, thereby obtaining the influence of upward seepage force on sediment initiation under wave flow conditions.

[0050] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A model test apparatus for analyzing the influence of seepage force on sediment initiation under wave-current action, characterized in that: include: The horizontal water tank device includes a first connecting part, a first rectifying part, a test observation part, a second rectifying part, and a second connecting part. The first connecting part and the second connecting part include water tank corner sections and are connected to wave-generating units and circulating water pipelines. The first and second rectifying parts are equipped with honeycomb rectifiers. The test observation part has a seepage force generating device detachably installed at the bottom. The wave-current generating device includes a wave-generating unit and a steady-flow circulation unit. The wave-generating unit is used to generate an oscillating water flow that simulates the action of waves, and the steady-flow circulation unit is used to simulate a steady water flow that simulates the action of ocean currents. The wave-generating unit controls the formation of oscillating flow through the combined reciprocating motion of the first piston and the second piston. The first piston is connected to the first connecting part, and the second piston is connected to the second connecting part. The two pistons are linked by a piston connecting rod. The amplitude and speed of the piston movement are controlled and adjusted by an electro-hydraulic servo system. A seepage force generating device is used to place sediment samples and generate seepage forces with a specified regular distribution. The seepage force generating device includes a silt tank, permeable stones, a second sealed water reservoir, a second ball valve, a second pressure gauge, and a second air compressor. A silt cushion layer is laid at the bottom of the silt tank, and permeable stones are covered on the silt cushion layer. The silt sample used to observe the silt initiation is laid on the permeable stones. A second ball valve connected to the second sealed water reservoir is provided at the bottom of the silt tank. The second sealed water reservoir is connected to the second air compressor to control the air pressure change, thereby changing the water pressure to control the magnitude of the seepage force. The data acquisition module is used to collect key variable data during the experiment and to photograph the sediment initiation situation for subsequent analysis. Simulation experiments were conducted using the above-mentioned apparatus. First, the valve at the bottom of the sediment tank was closed to prevent seepage force. Under the designed water depth and wave flow conditions, the sediment initiation was captured using a high-definition digital imaging device. The flow velocity distribution and pore pressure changes at the positions of the first and second pore water pressure gauges were collected. The pressure gradient was obtained by subtracting the data collected by the two pore water pressure gauges, and thus the seepage force change curve was plotted. Subsequently, the experiment was repeated, maintaining a stable flow while stopping the piston reciprocating motion to obtain the sediment initiation under stable flow conditions. The valve at the bottom of the sediment tank was opened, and the air pressure change was controlled to generate calculated seepage force. The sediment initiation distribution under the action of stable flow plus seepage force was obtained and compared with the sediment initiation under stable flow and wave flow conditions.

2. The model test apparatus for analyzing the influence of seepage force on sediment initiation under wave-current action as described in claim 1, characterized in that: The stable flow circulation unit maintains a stable water flow through a circulating water system. The stable flow circulation unit includes a first sealed water tank, a first air compressor, a circulating water pump, a flow meter, a one-way valve, and a circulating water pipeline. The first air compressor is connected to the first sealed water tank through an air pipeline. By changing the air pressure, the water pressure conditions are controlled to simulate the wave effect at different depths.

3. The model test apparatus for analyzing the influence of seepage force on sediment initiation under wave-current action as described in claim 1, characterized in that: The test observation section is detachable at both ends and bottom, and is connected to the rectifier section and the sediment tank by bolts and sealing rings; the first connecting part, the second connecting part, the first piston, the second piston and the circulating water pipeline are connected, and the connection is sealed.

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